1. Field of the Invention
The present invention relates to a method for forming a filter in a fluid flow path in a microfluidic device.
2. Description of the Related Art
Microfluidic devices, e.g., compact disc (CD)- or microchip-type microfluidic devices, are often used in biological analysis. In the biological analysis employing a microfluidic device, spherical particles or beads are widely used for performing various functions in the analysis of a biological sample, such as cells, proteins, nucleic acids, or the like. It is necessary to isolate the beads, once used, from a sample solution. In order to isolate the bead, centrifugation or filtration may be employed.
Meanwhile, it is quite difficult to form a filter, i.e., a porous substance for performing desired filtering, in a microfluidic device because a microchannel generally has a small dimension, for example, of 500 μm or less. That is to say, it is difficult to accomplish inserting a filter into a microchannel of such a small dimension. Furthermore, it is difficult to insert a filter into an appropriate location of a microchannel. It is also difficult to hermetically seal a filter inserted into a microchannel.
U.S. Pat. No. 6,811,695 discloses a microfluidic device incorporating a filter element, the microfluidic device comprising: a first substantially planar device layer defining a microfluidic inlet channel; a second substantially planar device layer defining a microfluidic outlet channel, the outlet channel, having a first height; a third device layer disposed between the first device layer and the second device layer, the third device layer defining an aperture disposed between the inlet channel and the outlet channel, the aperture having a first width; and a filter element having a second height and a second width, the filter element being disposed substantially within the microfluidic outlet channel adjacent to the aperture; wherein the second height is greater than the first height, the second width is greater than the first width, and the filter element is compressively retained between the second device layer and the third device layer. U.S. Pat. No. 6,852,851 discloses a method of isolating DNA or cell nuclei or a mixture thereof from cells, which method comprises: a) treating a suspension of whole cells with a lysis reagent so as to lyse the cytoplasmic membranes and at least some of the nuclear membranes; b) introducing the resultant lysate from step a) into micro-channels of a microfabricated apparatus wherein each of said micro-channels incorporates means to impede the passage or flow of DNA and cell nuclei while allowing the passage of liquid through the micro-channel whereby a mesh comprising DNA is formed in the channel; and, c) washing the mesh comprising DNA. U.S. Pat. No. 7,279,134 discloses a microfluidic device, comprising a substrate platform comprising a plurality of cascading microfluidic channels including respective pairs of upper and lower microfluidic channels; and a plurality of porous membranes, each disposed between end portions of a respective pair of upper and lower microfluidic channels and comprising a semi-permeable barrier having a plurality of pores to selectively filter an influent fluid that may be introduced in an upper microfluidic channel on an input side thereof to produce a filtered effluent fluid in the lower microfluidic channel on an output side thereof.
Despite these and other attempts, still further methods for efficiently forming a porous membrane, i.e., a filter, in a microfluidic device, is desired.